The present invention relates to processes and composition based zeolites of type A, the exchangeable cation sites of which are occupied by sodium, potassium, calcium and/or magnesium and hydronium ions, which are particularly effective in formulations based on polyurethane (PU) resins as regards limitation of gaseous inclusions and influence on the potlife.
Two-component non-cellular polyurethanes (PU) are resins which are widely used, in particular in the varnish, adhesive, film and coating industry. The surface appearance is a very important characteristic for these applications. These polyurethanes are prepared by addition of di- or polyhydroxyl compounds to di- or polyisocyanates. In point of fact, at the same time as the formation of the urethane bonds, the isocyanates react with the water present in the reaction medium, giving rise to hydrolysed isocyanates which are no longer available for polymerization of the PUs and themselves give rise to carbon dioxide, which, during its release, will create bubbles in the PU and will thus greatly modify, in a harmful fashion, the surface condition of the final PU.
As the hydroxyl compounds available industrially comprise, depending upon their source and their quality, up to 5% by weight of water, it is necessary to prevent the reactions of the isocyanates with the water by adsorbing the water present in the hydroxyl compounds using a suitable drying agent.
FR 1 321 178 or U.S. Pat. No. 3,326,844 discloses the use of zeolite 4A (zeolite of type A, essentially all the exchangeable cationic sites of which are occupied by Na+), zeolite 5A (a portion of the cationic sites is occupied by Ca2+, the remainder of the sites being at least predominantly occupied by Na+) and zeolite 13X (NaX) for drying PU resins; these zeolites exhibit the advantage of adsorbing water but the disadvantage of also adsorbing nitrogen, which can be desorbed over time, thus leading to bubbles and gaseous inclusions in the PU resin.
FR 2 049 873 or DE 1 928 219 discloses a process for the preparation of non-cellular PU bodies comprising, as drying agent, a zeolite 3A, 5 to 40% of the cationic sites of which are occupied by sodium ions and 95 to 60% by potassium ions. In point of fact, it has been found that zeolite 3A does not truly constitute an inert filler with regard to the polymerizable system and that, after prolonged storage of the hydroxyl compound with zeolite 3A, it happens that the potlife of the hydroxyl compound/isocyanate compound system is found to be greatly reduced to the point of being too short for correct application of the PU. U.S. Pat. No. 6,051,647 discloses a process for preparing a zeolite of type A, the exchangeable cationic sites of which are occupied by K+, Na+ and H+ cations, from a zeolite 3A (i.e., the exchangeable cationic sites of which are occupied either by potassium ions or by sodium ions) which is treated with an acidic solution so that the pH of this zeolite is between 9.6 and 11. Such a zeolite makes it possible to increase the potlife of PU formulations with respect to that of PU formulations comprising a zeolite 3A. EP 346 604 shows that a zeolite 3A, treated with an acidic solution so that the pH of this zeolite is between 7.5 and 9.5, makes it possible to consequently increase the potlife of PU resins but U.S. Pat. No. 6,051,647 and EP 346 604 are silent on the ability to adsorb nitrogen by these zeolites.
EP 239 706 or U.S. Pat. No. 4,857,584 discloses, as drying agent for PUs, a zeolite of type A, the cationic sites of which are occupied by Ca2+, K+ and Na+ or Mg2+, K+ and Na+, which is an improvement with respect to zeolites 4A, 3A and 13X as it makes it possible not only to prevent the evolution of CO2 but also the evolution of nitrogen. The potlife of the PUs treated with this additive, although substantially improved with respect to the prior technical solutions, is still insufficient for the requirements of formulators of PU resins.
Accordingly, an object of this invention is to provide an improved zeolite having a zeolite A structure which will avoid at least one of the above described disadvantages.
Another object is to provide a process for producing the improved zeolite A.
Still another object is to provide polyurethane formulation with the comprised zeolite.
Upon further study of the specification and appended claims, further objects and advantages of this invention will become apparent to those skilled in the art.
To obtain the above objects, there are provided zeolites of type A with an Si/Al atomic ratio of between 0.95 and 1.1, all the cationic sites of which are occupied by sodium, calcium and/or magnesium, potassium and hydronium cations, comprising, given in equivalents:
from 10 to 69%, preferably from 20 to 55%, of sodium ions,
from 28 to 55%, preferably from 28 to 40%, of potassium ions,
from 2 to 45%, preferably from 10 to 45% and advantageously from 15 to 45% of calcium and/or magnesium ions,
and from 1 to 20%, preferably from 2 to 10% and advantageously from 3 to 6% of hydronium ions,
the sum of the sodium, potassium, calcium and/or magnesium, and hydronium cations (given in equivalents) being equal to 100%, which exhibit the advantage of having a water adsorption capacityxe2x89xa723%, which do not adsorb and therefore cannot desorb nitrogen, and which, incorporated in PU resins, make it possible to increase the potlife of the PU formulations in which they are incorporated to a markedly greater extent than the zeolitic drying agents as defined in EP 239 706 while not being very sensitive to the age of the hydroxyl compound.
To produce the improved zeolitic drying agent, there is provided a process comprising 1/ bringing the following aqueous solutions or suspensions into contact:
a-i an aqueous suspension of zeolite 3A(a-1), 4A(a-2) or 5A(a-3),
b-j an aqueous solution of calcium salt(s) (b-1), or of potassium salt(s) (b-3), or solutions of calcium and potassium salt(s) (b-2),
c an acid solution
according to one or other of the following methods:
either a-i, b-j and c simultaneously
or a-i and b-j, then c,
or a-i and c, then b-j,
or b-j and c, then a-i,
with, in all cases, i and j being identical (which will be indicated subsequently by a-i and b-i, in other words a-1 and b-1 or a-2 and b-2 or a-3 and b-3 can be carried out but not for example a-1 and b-2, a-3 and b-1, etc.),
2/ then filtering off and washing the solid obtained,
3/ then drying and activating, preferably by flushing with a nondecomposing gas, the solid resulting from 2/.
The proportions of the various cations present in the structure of the zeolites are measured conventionally by X-ray fluorescence, the accuracy of the measurements being of the order of 1%.
The term xe2x80x9czeolite 4Axe2x80x9d is understood to mean here a zeolite of type A, essentially all the exchangeable cationic sites of which are occupied by Na+.
The term xe2x80x9czeolite 3Axe2x80x9d is understood to mean here a zeolite of type A, 28 to 60% (given in equivalents) of the exchangeable cationic sites of which are occupied by potassium ions, the remainder of the sites being occupied by Na+.
The term xe2x80x9czeolite 5Axe2x80x9d is understood to mean here a zeolite of type A, at least 40% (given in equivalents) of the cationic sites of which are occupied by Ca2+, the remainder of the sites being occupied by Na+.
Within the meaning of the invention, the term xe2x80x9csolutions (b-2)xe2x80x9d, is understood to mean not only solutions which comprise calcium salts and potassium salts but also the combination of a solution of calcium salt(s) (b-1) and of a solution of potassium salt(s) (b-3) with which the reactants (a-2) and (c) are brought into contact: either brought into contact with (b-1) and then with (b-3) or brought into contact with (b-3) and then with (b-1); in other words, in the context of the process according to the invention, (b-2) should also be understood as (b-1) then (b-3) and (b-3) then (b-1).
Within the meaning of the invention, the term xe2x80x9cacid solution (c)xe2x80x9d should be understood as meaning aqueous solutions of weak and/or strong acid(s), preferably based on strong acid(s), such as sulphuric acid, hydrochloric acid and/or nitric acid, with a normality generally of between 0.1N and 36N and preferably of between 0.5 and 10N.
When the solutions and the suspension are brought into contact simultaneously [(a-i) and (b-i) and (c)], the mixing is generally carried out for a time of less than 1 hour at a temperature generally of between 15 and 80xc2x0 C.
In the case where, in a first step, the zeolite suspension (a-i) and the acid solution (c) are mixed, the mixing is generally carried out for a few minutes, preferably with stirring, before introducing the saline aqueous solution (b-i), the reaction mixture then being stirred for a time generally of less than 1 hour at a temperature generally of between 15 and 80xc2x0 C.
In the case where, in a first step, the solution of salt(s) (b-i) and the acid solution (c) are mixed, the mixing is generally carried out for a few minutes, preferably with stirring, before introducing the zeolite suspension (a-i), the reaction mixture then being stirred for a time generally of less than 1 hour at a temperature generally of between 15 and 80xc2x0 C.
In the 3 cases described above, a solid in suspension is obtained, which solid is filtered off and then washed with water.
In the case where, in a first step, the zeolite suspension (a-i) and the solution of salt(s) (b-i) are mixed, the mixing is generally carried out for a time generally of less than 1 hour, preferably with stirring, and at a temperature generally of between 15 and 80xc2x0 C.; a suspension of a solid is then obtained, which solid is filtered off and washed with water before being introduced into the acid solution (c), and then the product is filtered off and washed with a mixture of the acid solution and of washing water.
The concentrations and compositions of the solutions of salts and of acid will be adjusted so that the final zeolite corresponds to the formula indicated previously without particular difficulty.
The inventors have found, from the syntheses which they have carried out, that at least 50% of the hydronium ions of the acid solution (c) are exchanged with the other cations present on the starting zeolite.
Once filtered and washed, the solid obtained is subjected to a heat treatment comprising first a stage of drying, generally between 60 and 110xc2x0 C., for a time generally ranging from approximately half an hour to approximately 2 h, followed by a stage of activation at a temperature generally of between 300 and 600xc2x0 C., preferably between 350 and 500xc2x0 C., which is particularly important for the final quality of the zeolite resulting from the process. The inventors have found that, surprisingly, the pH of the zeolites thus prepared increases when the activation temperature increases but also that an increase in the temperature increases the decomposition in crystallinity of the zeolite. Preferably, the activation stage is carried out under gaseous flushing with a nondecomposing gas (air, N2, and the like) which makes it possible to rapidly discharge the water present in the zeolite to prevent its hydrothermal decomposition while limiting the negative effects, indicated above, due to an excessively high activation temperature.
The amount of acid is adjusted so that an activation of between 300 and 600xc2x0 C., preferably between 350 and 500xc2x0 C., under gaseous flushing makes it possible to obtain a final product of good quality for the application of drying polyurethanes (water adsorption capacityxe2x89xa723% (corresponding to the ratio of the increase in the mass of 1 g of activated zeolite after saturation with water on conclusion of a stay of 24 h in a closed chamber at 23xc2x12xc2x0 C., the relative humidity of which is equal to 50%, to the mass of reference activated zeolite (in this instance 1 g)xc3x97100) and pH of between 9.5 and 10.5, measured according to Standard NF EN ISO 787-9:1995). It is found that the more acid (solution c) is added with respect to the starting zeolite present in the suspension (a-i), the lower the pH of the final zeolite and the more the crystallinity of the final zeolite is also found to be reduced.
The resultant zeolites are used in the same manner. Other zeolite A products are used in the prior art, especially for the production of polyurethanes.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.
In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.
The entire disclosures of all applications, patents and publications, cited above or below, and of corresponding French application No. 01/00325, filed Jan. 11, 2001 is hereby incorporated by reference.